Multimodal interactions in Stomoxys navigation reveals synergy between olfaction and vision

Background:

Pathogens are transported from one environment to another or to different organisms through vectors, typically disease-carrying insects that serve as carriers for parasitic microbes. Stomoxys flies fall into this category of vectors, thriving in the blood and skin of their animal hosts. They exert both direct and indirect effects on their targets. While they indirectly transmit pathogens through mechanical means, they also directly cause issues such as skin lesions, blood loss, and immunosuppression (Baldacchino et al., 2013). Given their role in transmitting various pathogens among livestock, it is crucial to develop methods for monitoring and controlling vector activity to reduce pathogenic transmission.

Understanding the sensory environment of vectors is an effective approach to target and control their activity. Once we know what attracts them, trapping them becomes more feasible. At different phases of their search for hosts, insect vectors employ multimodal signals, including host scent, color, morphology, auditory cues, gustatory signals, and mechanosensory signals. A sophisticated sensory system helps them minimize errors and make accurate decisions when locating their blood meal source (Murlis et al., 1992).

So, the authors of this preprint researched the sensory environment of these flies with the aim of creating effective traps that specifically amplify the sensory responses of Stomoxys flies.

Key findings:

• The wavelength of the skin color in livestock and the nectar source of plants varies.
  Since Stomoxys flies feed on blood of livestock and nectars of certain plants, the authors measured the reflectance of skin of different cattle phenotypes to test the potential role of various livestock fur colors in influencing stable fly-livestock interactions and found a huge variation in the spectrum. The reflectance steadily increased from 300 to 700 nm and showed no spectral peak data.

Figure 1. Livestock fur Skin color and nectar source of plants and the corresponding fabric color to represented livestock and plants parts. (A) Photo showing the various color phenotypes of livestock, blood meal source of Stomoxys (B) nectar source (Photo icipe/MNG). (C) The various fabric colors used for behavioral evaluation. (D) spectrophotometer measurement from selected livestock fur colors and selected used fabric colors. The number matching shows how the authors represented animals’ fur and plant colors with fabric colors.

 

• Stomoxys flies exhibit an attraction to adhesive targets of different colors.

Following that, the researchers proceeded to examine additional colors that closely resembled the host, blood meal, and nectar source colors to enhance the efficacy of trapping these vectors. Among the tested colors, sticky targets with red coloration, followed by khaki, blue, and white/grey, demonstrated higher attractiveness to Stomoxys spp. compared to the other colors assessed.

• Nanopolymer beads were engineered to form robust strands and facilitate the controlled release of semio-chemicals.
  Following their observations that red and blue colored cotton-polyester fabric traps were sufficiently attractive to trap these flies, the scientists used nanopolymer beads with host odors for vector trapping. A blend of odors from gravid females and blood meals were found to be very effective in comparison to the wax formulation control. 

• The combination of visual and olfactory signals enhanced the effectiveness of trap captures.

The trap was integrated with red color and host odors. A blend of carvone and p-cresol was given to target both blood meal searching as well as gravid females. This significantly enhanced the success of the traps relative to the pure host odor that was given. 

• The appeal of the red Vavoua trap is unaffected by ecological factors.

To explore the influence of ecological conditions on the morphological characteristics of the trap, Getahun and colleagues tested the traps in both semi-arid and coastal environments. Despite the traps being situated in distinct ecological settings, the researchers observed that the red fabric exhibited the highest level of attractiveness.

What I like about the preprint?

I appreciate this paper for tackling the primary concern of vector management. The fact that Stomoxys flies exhibit attraction towards objects without any tangible rewards, such as traps and targets without blood or nectar incentives, is intriguing. The authors also raise a crucial point about the development of target-specific traps to minimize the inadvertent capture of non-target insects, thereby delving into the conservation perspective.

Future directions:

This work sheds light on many interesting facts about the sensory ecology of flies. Although the authors have methodically investigated the most appealing stimuli for Stomoxys flies and devised effective traps, it would be intriguing to conduct context-based comparative behavioral assays. Such assays could assess how these flies respond when presented with a choice among various attractants in hunger-inducing situations. It is widely acknowledged that insects are drawn to food odors and mate odors based on their specific needs.

Additionally, exploring the neural underpinnings of this behavior could shed further insights into multimodal sensory processing. Recording from neurons that respond to these stimuli while the flies approach the traps would provide valuable insights into the neural mechanisms at play.

References:

1. Murlis J, Elkinton JS, Cardé RT. 1992 Odor plumes and how insects use them. Annu Rev Entomol 37, 505–532. (doi:10.1146/annurev.en.37.010192.002445) 
2. Changbunjong. T, Sumruayphol. S , Weluwanarak. T, Ruangsittichai. J, and Dujardin . J, (2016) Landmark and outline-based geometric morphometrics analysis of three Stomoxys flies (Diptera: Muscidae). Folia Parasitologica 63: 037

Tags: cues, odor, pathogens, vision

doi: https://doi.org/10.1242/prelights.36413

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